Several known e-mail systems provide facilities to incorporate one or more attachment files into an e-mail message to be transmitted from a sender to a recipient. Attachments may be formatted, for example, as specified in RFC-1341 MIME (Multipurpose Internet Mail Extensions): Mechanisms for Specifying and Describing the Format of Internet Message Bodies.
In known e-mail systems, attachments are typically incorporated into an e-mail message by the mail user agent (MUA)—the program which provides a mail sending and receiving user interface to the mail user—either at the time the attachment is identified by the user to the MUA, or at some other time before the message is released for transmission.
In a typical computing environment in which the user employs a personal computer workstation, the MUA is a conventional e-mail program, such as Mozilla Thunderbird, Microsoft Outlook, or the like, which may have direct access to files on one or more of local storage devices and network storage. Incorporating an attachment into an e-mail message involves adding one or more e-mail headers signaling that attachments are present and identifying a boundary token (if the attachment is the first attachment), retrieving the attachment from storage, encoding the attachment in a format appropriate for the data contained in the attachment, appending an attachment preamble to the message, appending the encoded attachment to the message, and appending an attachment postamble to the message. Once assembled, the complete e-mail, including all attachments, is transmitted as a unit by the MUA. The MUA runs as a non-privileged program under the user's credentials on the user's computer and therefore has direct access to the same files on local and network storage that the user and other ordinary programs running on his behalf would have.
In recent years, wireless hand-held devices (WHHD) that provide a number of services, including e-mail, have become popular and useful. Although a number of network topologies are possible, one advantageous arrangement employs a hand-held device operatively coupled via one or more wireless network links to enterprise networks or application service providers, which offer a variety of application services, including e-mail. The wireless network links may employ any of a number of technologies, including without limitation the family of technologies referred to as WiFi, carrier-operated wireless data networks, such as those operating as part of or overlaid on cellular telecommunications networks of any generation, and the like. In addition to the wireless component, the network path between the WHHD and the enterprise network or application service provider may involve additional network media, including the internet and private network facilities, and may involve multiple carriers and other service providers.
A disadvantage of conventional MUAs when used with a WHHD is that transmission of large e-mails containing attachments requires transfer of large amounts of data via the wireless network. Each attachment file must traverse the wireless network at least twice: a first time when retrieved by the MUA for attachment to the e-mail message, and a second time as part of the transmitted e-mail message. The network path between the WHHD and the enterprise network of application service provider may be capacity-limited, slow, expensive, or high in latency. Thus, transmitting large e-mails containing attachments could involve expenses and delays which are unacceptable to users, carriers, and service providers.
In a known e-mail arrangement for WHHDs, an e-mail message containing an attachment and received on behalf of the user may be forwarded at the request of the user to another recipient without transmitting the entire attachment to the WHHD, and without the WHHD itself retransmitting the attachment as part of the forwarded e-mail message. A modified version of the attachment suitable for display to the user on the HHD may be transmitted to the HHD, but the entire attachment is retained in storage of an enterprise e-mail application server. However, this arrangement only provides capabilities for forwarding e-mails that already contain attachments, which are retained in the enterprise e-mail application server. It does not provide the capability to add arbitrary attachments—i.e., attachments which may be freely selected by the user from any files accessible thereto, which have not arrived as an attachment to a prior e-mail message, and which are not retained in the enterprise e-mail application server—or to send attachments with new, non-forwarded e-mail.
Thus, there is a need for an e-mail system for use with wireless handheld devices that allows the attachment to e-mail messages of files arbitrarily selected by the user while minimizing transport of attachment content over the wireless network.